Table of Contents  
CASE REPORT
Year : 2016  |  Volume : 12  |  Issue : 2  |  Page : 69-71

Ulnar nerve compression by accessory abductor digiti minimi muscle


Department of Plastic Surgery, Sri Ramachandra University, Chennai, Tamil Nadu, India

Date of Web Publication17-Mar-2017

Correspondence Address:
Bellam Alagirisamy Ramesh
Department of Plastic Surgery, Sri Ramachandra University, No. 1, Ramachandra Nagar, Porur, Chennai 600116, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0794-9316.202440

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  Abstract 

We report two cases of accessory abductor digiti minimi muscle causing ulnar nerve compression at the Guyon’s canal. One case had venous malformations on the palm with gangrenous left little finger terminal phalanx. Excision of the abnormal muscle relieved patient symptoms. Though the abnormal muscle is reported in literature, the number of symptomatic clinical cases due to muscle compression is rare. The diagnosis itself might be missed because of lack of awareness.

Keywords: Accessory abductor digiti minimi, gangrene little finger, Guyon’s canal compression, ulnar nerve compression, venous malformation


How to cite this article:
Mohan J, Ramesh BA. Ulnar nerve compression by accessory abductor digiti minimi muscle. Nigerian J Plast Surg 2016;12:69-71

How to cite this URL:
Mohan J, Ramesh BA. Ulnar nerve compression by accessory abductor digiti minimi muscle. Nigerian J Plast Surg [serial online] 2016 [cited 2021 Mar 2];12:69-71. Available from: https://www.njps.org/text.asp?2016/12/2/69/202440


  Introduction Top


The majority of accessory abductor digiti minimi muscles are asymptomatic and tend to be noticed by accidental discovery during surgery or during imaging examination. The patient may complain of sensation of pins and needles, pain on palm with sensory loss on the little finger and ulnar aspect of the ring finger, and weakness of the intrinsic muscles. The treatment is early diagnosis and excision of the muscle. We present two clinical cases of Guyon’s canal syndrome by the accessory muscle.


  Cases Top


A 26-year-old male, who was a carpenter and a nonsmoker, presented with a blackish discoloration on the distal portion of the left little finger for 3 weeks. He had pain on the nondominant, left little and ring fingers for 1 month. He also had a swelling on the medial border of the left palm for 6 months and complained of difficulty in using the left hand. On examination, he had a soft, compressible and nontender swelling on the hypothenar eminence. The terminal phalanx of the left little finger was gangrenous. Clawing of the little and ring fingers with wasting of intrinsic muscles was noted. Both radial and ulnar pulses were felt, and they were normal. A Doppler ultrasound investigation showed venous malformation on the left palm extending up to the proximal phalanx of the little finger. A nerve conduction study revealed decrease in transmission of the ulnar nerve at the Guyon’s canal region. The provisional diagnosis was venous malformation of the palm compressing neurovascular structures. On exploration, venous malformations extending from the mid palm to the proximal phalanx of the little finger coursing via the ulnar border of the palm was found and excised. Both digital vessels to the little finger needed to be sacrificed during malformation removal; hence, the left little finger was amputated to the level of metacarpophalangeal joint. On dissection of the Guyon’s canal, an accessory abductor digiti minimi muscle was found to arise from the palmaris longus tendon and also from the surrounding deep fascia. The abnormal muscle crossed over and compressed the left ulnar neurovascular bundle. There were no venous malformations as suspected preoperatively inside the Guyon’s canal. The abnormal muscle was inserted into the abductor digiti minimi muscle belly [Figure 1]. The accessory abductor digiti minimi was removed from the site of origin to the site of insertion. The intrinsic muscles recovered 6 months after surgery, and sensation on the ring finger improved.
Figure 1: First patient

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Second patient

A 35-year-old male, who was an electrician and a nonsmoker, had sensation of pins and needles along the ulnar nerve distribution of the left palm for 1 month. His right hand was dominant. A nerve conduction test revealed compression of the ulnar nerve at the Guyon’s canal region. The compound action potential amplitude was reduced more than 40% distal to the Guyon’s canal when compared proximally. The patient was planned for surgical decompression of the tunnel. At exploration, an accessory abductor digiti minimi muscle was found to arise from the forearm fascia ulnar to the palmaris longus tendon and running over the Guyon’s canal and inserting into the abductor digiti minimi muscle belly [[Figure 2]A and [Figure 2]B]. The abnormal muscle from the site of origin to the site of insertion was excised. The pain on the left palm waned after surgery.
Figure 2: Second patient

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  Discussion Top


Ulnar tunnel syndrome, which is compression of the ulnar nerve at the Guyon’s canal, is usually caused by a ganglion cyst, schwannoma, vascular malformation, edema due to rheumatoid arthritis synovitis, carpal bone fractures, vibratory injury, or an abnormal muscle. Compression by an accessory muscle is commonly missed. Accessory abductor digiti minimi is described in anatomic, surgical, and radiological literature. It is incidentally found by ultrasound or magnetic resonance imaging investigations and is most often asymptomatic. Cadaveric dissection revealed prevalence of accessory abductor digiti minimi in 24% of the population.[1] Harvie et al. found an accessory abductor digiti minimi muscle in 41 of 116 (35%) volunteers on ultrasound examinations. It had greater prevalence in men, and 50% of the cases were bilateral.[2] The muscle originates from the antebrachial fascia of the forearm, the palmaris longus tendon, or the flexor retinaculum and inserts into the abductor digiti minimi muscle belly.[2],[3] There were 25 published clinical case reports of accessory abductor digiti minimi from 1813.[4] In our series, both cases had compression of the ulnar neurovascular bundle because of accessory abductor digiti minimi muscles. Gangrene of the finger in the first case report could be explained by thrombosis of the vessels by compression from venous malformation at the level of the proximal phalanx. The accessory abductor digiti minimi muscle associated with vascular tumor is a rare presentation.


  Conclusion Top


In the diagnosis of low ulnar nerve palsy, accessory abductor digiti minimi muscles should be considered as a differential diagnosis; this requires a high index of suspicion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Siva Prasad GV, Sailaja XX, Asha Latha D. Accessory abductor digiti minimi − A case report. IOSR J Dent Med Sci 2015;14:4-6.  Back to cited text no. 1
    
2.
Harvie P, Patel N, Ostlere SJ. Prevalence and epidemiological variation of anomalous muscles at Guyon’s canal. J Hand Surg Br 2004;29:26-9.  Back to cited text no. 2
    
3.
Curry B, Kuz J. A new variation of abductor digiti minimi accessorius. J Hand Surg Am 2000;25:585-7.  Back to cited text no. 3
    
4.
Uzel AP, Bulla A, Joye ML, Caix P. Variation of the proximal insertion of the abductor digiti minimi muscle: Correlation with Guyon’s canal syndrome? Case report and literature review. Morphologie 2012;96:44-50.  Back to cited text no. 4
    


    Figures

  [Figure 1], [Figure 2]



 

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